A fermentative production process of chemicals from sugar as a raw material has been employed to produce various industrial raw materials. Sugars currently used as the raw materials for industrial fermentation are derived from edible materials such as sugar cane, starch, and sugar beets. From the viewpoint of a rise in prices of the edible raw materials due to the increase in global population in the future or competition with foods, a future subject is to construct a sugar solution production apparatus that further efficiently produces a sugar solution from a renewable inedible resource, that is, a cellulose-containing biomass or to construct a sugar solution production system that efficiently converts the obtained sugar solution as a fermentation raw material into an industrial raw material.
A cellulose-containing biomass is mainly composed of lignin that is an aromatic polymer and cellulose and hemicellulose that are monosaccharide polymers. A typical method of obtaining a sugar solution includes subjecting cellulose and hemicellulose protected by lignin to a mechanical or thermochemical pretreatment process, for example, a pulverization treatment and a treatment with hot water at high pressure and high temperature, diluted sulfuric acid, or ammonia (for example, see Japanese Patent Application Laid-open No. 2009-183805 and Japanese National Publication of International Patent Application No. 2008-535523) to remove the lignin and then hydrolyzing the cellulose and the hemicellulose with a saccharifying enzyme to produce monosaccharides.
Among them, the process of producing monosaccharides by hydrolyzing cellulose and hemicellulose with a saccharifying enzyme involves an economic problem. For example, the saccharifying enzyme is very expensive. In addition, a cellulose-containing biomass is saccharified with a saccharifying enzyme at a lower efficiency than that of starch, thus the hydrolysis reaction requires a long period of time from a day to several days, and this increases the cost.
To address this problem, reuse of such a saccharifying enzyme has been tried in the process to reduce the cost required for the saccharification. An example is a method of recovering a saccharifying enzyme by membrane separation from a sugar solution obtained (for example, see Japanese Patent Application Laid-open Nos. 61-234790 and 2011-139686). However, most saccharifying enzyme is adsorbed onto a decomposed residue, which is a solid substance after the hydrolysis reaction, and thus such a saccharifying enzyme fails to be thoroughly recovered by such a method as the membrane separation. Disclosed methods to solve the problem are, for example, a method of desorbing a saccharifying enzyme adsorbed onto a saccharified residue by washing the residue and reusing the enzyme (for example, see Japanese Patent Application Laid-open Nos. 63-87994 and 2010-36058) and a method of reusing a saccharifying enzyme by returning a decomposed residue after solid-liquid separation to a saccharification reaction tank (for example, see Japanese Patent Application Laid-open Nos. 2010-17084 and 2011-19483).
However, the method of obtaining a sugar solution and a saccharifying enzyme from a saccharified solution as described in JP '994 has the following problems: For example, the washing requires a large amount of water; the sugar concentration of the sugar solution is greatly lowered; and an agent for desorbing the saccharifying enzyme cannot be used in a large amount because the agent is to be contained in the sugar solution. In addition, the method requires a tank and a stirrer for the washing, and this increases the cost of equipment.
In the saccharification system described in JP '058, the solid substance is taken out of a solid-liquid separation apparatus, and thus a larger amount of water is required to wash the residue with. In addition, several solid-liquid separators are required. Consequently, the cost of equipment increases.
The saccharification and fermentation system described in JP '084 and the method of producing a sugar solution described in JP '483 also have following problems: For example, returning a saccharified residue to a saccharification tank causes the accumulation of an undecomposed residue mainly derived from lignin to hinder continuous operation; and a discharged residue contains both an undecomposed material and a decomposed material to substantially reduce the saccharification rate. Such problems make the saccharification system itself complicated, thus increasing the cost of equipment.
In view of the above problems, it could be helpful to provide a sugar solution production apparatus and a sugar solution production system that can efficiently produce a sugar solution at low cost while efficiently recovering a saccharifying enzyme.